Pump control



06f' 9,1951 .Y F. T.HARR1NGTON 2,570,342

PUMPl CONTROL Filed Nov. 26, 1945 INVENToR. FgH/zs Thum/Grow Patented ct. 9, 1.951

PUMP CONTROL Ferris T. Harrington, Detroit, Mich., assignor` to v Vickers Incorporated, Detroit, Mich., a corporation of Michigan Application November 26, 1945, Serial No. 630,919

. This invention relates tovpower transmissions, particularly to. those of. the type comprising two or more uid pressure energy translating devices, one of which may function as a pump and another as a uid motor.

Y. The Yinvention kis more particularly concerned witha power transmission system incorporating a plurality of pumps such, for exampie, as are found aboard aircraft. In some A installations where a wide variety of hydraulically-operated devices are connected foroperation from a centralV pressure system, the volumetric demands on that system uctuate widely; for example, in a large aircraft the volumetric requirements for pressurefluid to operate such devices as landing gear retraction cy1inders,wing flaps, bomb bay doors, etc., arerquite large but are only required to be operated intermittently at long intervals. Other devices,y such as night-control boosters, .automaticpilots etc., require relatively small volumes but Aoperate continuously for long periods. ,l j `Where the pressure source for such a system constitutes one or more xed displacement pumps provided with the usual pressure-responsive ,unloading valvekandv accumulator, the pump and accumulator capacity must be sufcient to take care of the momentary large volume requirementsand these requirements, in fact, determine the design characteristicsof the pressure source. vSuch a system, however, is not particularly well adapted to supply small volume requirements continuously inasmuch as the pressure differential of the unloading valve makes it impossible to provide iluid continuously at a uniform pressure. Also, the surges which result from the sudden opening or closing of the unloading valve of large capacity are sometimes undesirable .when a small Avolume device is in operation, particularly a. sensitive one such as .an automatic pilot or. control booster. y

i ,.It is an` object of .thepresent invention, there fore, to provide an improved pressure source capable of meeting intermittent large-volume requirements and continuous small-volume requirements at -steady pressure.

It is also an object to provide such a system wherein a large fixed-displacement pump, unloading valve and accumulator are provided for supplying intermittently those operating devices requiring large volume together with a smallvolume, variable displacement, pressure-controlled pump capable of supplying small volumes at a steady pressure continuously.

It is a further object to provide a system of 2 Claims. (Cl. 10S- 11) 2 this character wherein the circuit connections are simple and reliable and wherein either Dump may automatically supply the system vin the event of failure of the other pump without the requirement of manual intervention.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanyingdrawing wherein a preferred form of the present invention is clearly shown. l

In the drawing the single iigure is a diagrammatic view of a hydraulic power transmission system incorporating a preferred form of the present invention.

Referring now to the drawing, there is shown an oil reservo-ir I0 having a line I2 leading lto a suction port of a large-volume, xed displacement pump I4. The delivery port of the pump Iiconnects bya conduit I6 with a pressure-responsive unloading valve I8 which has its return port connected to the reservoir IE) by a conduity 2 0., The System port of valve I8 leads by a conduit 22 to a T 24 connecting with the main supply line 26. The latter has an overload relief valve 28 connected therein having its overow port connected to the reservoir by a conduit 30. `Td into the main pressure line 28 is a pair of air-loaded accumulators 32.

Also leading from the reservoir I0 is a suction conduit 34 leading to the inlet port of a smallvolume, variable displacement pump 36. The pump :itis` of the type provided with a pressureresponsive, displacement regulator which, when the system pressure builds up to a predetermined value, begins to reduce the displacement of pump v36 and, upon a slight further rise, is capable of reducing the displacement substantially to zero. The delivery port of pump 36 connects by a conduit 38 having a check valve Ml therein to the T 2A.v The pumps I4 and 35 may be driven from any suitable prime mover on either a singleengine orY a4 multi-engine ship, preferably from separate engines.

y Y The unloading valve I8 may be of any conventional construction wherein, upon the sys- ,tem` pressure building up to a predetermined point, they delivery of pump I4 is bypassed to the reservoir Il] through conduit 2Q, an internal check valve. preventing backow from the delivery conduit A22. Upon the drop of system pressure to a predetermined value below the cutout point, the unloading valve will cut in by closing the bypass, causing the pump delivery to be directed to the system. 'I'he pressure settings of unloading valve I8 and pump 36 are arranged so that the cut-out point of unloading valve I8 is slightly below the point at which the pressure regulator of pump 36 begins to reduce the pump stroke.

There are shown on the drawing diagrammatically the elements of a typical hydraulic system including a four-way selector valve 42 for controlling al plurality of piston-and-cylinder uid motors 44 connected in'parallel and representing the type of load which is operated only intermittently at infrequent intervals and which, when operated, requires a substantially large, volume of fluid. There is also shown a control booster comprising a servo valve 46 and booster cylinder 48 together with aV floating lever, followup control 50 which is representative of the type of load requiring only a smallvolume,v but requiring it continuously overl long periods. A return line 52 leads from the exhaust ports of the valves 42 and 46 back tothe reservoir l0.

In operation with the system filled with oil and pumps i4 and 36 operating when the four- Way valve 42 is shifted to cause operation of the motor 44, the volumetric requirements are so great that oil is withdrawn from the pressure line 26 and accumulators 32 at a rate great enough to drop the pressure in the line 26 below the cut-in point of unloading valve I8 rather promptly after the valve 42 is shifted. Under these conditions pump 36 is at full displacement and pump I4 has itsentire volume directed through line 22 to line 26 so that motors 44 are supplied with the full volume of both pumps plus whatever additional volume may be required from the accumulators 32'.

When the motors 44 have reached the ends of their stroke, the full delivery of both pumps continues to be directed into line 26 and the accumulators 32 until the pressure reaches the cut-out point of unloading valve I8. Thereupon the valve I8 unloads pump I4 and pump 36 continues in operation additionally charging the accumulators until its own regulator begins to reduce its displacement.

When the booster system 46 and 48 is in operation itsi'luid requirements are amply met by the pump 36 and-its self-contained regulator adjusts its displacement so that it delivers only the quantity of oil consumed by the booster system plus r any leakage make-up requirements. Thus, when the large-volumedevices are not being operated, pump I4 may remain unloaded continuously and pump 36 automatically takes over the supply of iluid to the booster system.

Itwill be noted that, in thel even of failure of veither pump, that Athe system may continue in operation. For example, in the event of failure of pumpv 36, the pressure in the main line 26 is prevented from escaping through pump 36 by the check valve 40 and pump I4, unloading valve I8 andaccumulator 32 maintain pressure in line 26 in conventional fashion, which can be used to operate the low-volume part of the system in such emergencies. Likewise, in the event of failure of pump I4 or unloading valve I3, the check valve therein prevents loss of pressure from thev main line 26 and pump 36 will continue supplying oil to the system. Under these conditions, of course, the fluid motors 44 will operate much more slowly, but no less positively, so that the pump 36 pro-"- vides a stand-by which is usable in such emergencyA While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. A pressure source for a hydraulic power sysd tem of! the type having a substantially continuous demand at low volume and an intermittent demand at large volume comprising in combination, a fixed displacement pump, unloading valve and accumulator of sufcient capacity to supply substantially the entire large volume demand, and a pressure-controlled, variable displacement pump of a capacity at least equivalent to the low volume demand and connected in parallel with the first pump, the unloading valve being adjusted to unload the rst pump at apressure lower than the pressure at which the second pump begins to operate at reduced displacement whereby the continuous demand may be suppliedv by the second pump and the rst pump may remain unloaded except during periods of large volume demand.

2. A pressure source for a hydraulic power system ofthe type having a substantially continuous demand at low volume and an intermitf tent demand at large volume comprising in com'- bination, a xed displacement pump, unloading valve and accumulator of suicient capacity` to supply substantially the entire large volume demand, a pressure-controlled, variable displace;- ment pump of a capacity at least equivalent to the low volume demand and connected'in parallel with the first pump, the unloading valve being adjusted to unload the first pump at a pressure lower than the pressure at which the second pump begins to operate vat reduced displacement whereby the continuous demand may bef supplied bythe-second pump and the ,first pump may remain unloaded except during periods oflarge volume demand, and a check valve in theA outlet of the second pump whereby inthe event of failure of either pump the other pump may rejmain operative to supply the entire system.

FERRIS TL HARRINGTON.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED. STATES PATENTS 

